HIGH STRENGTH, LOW CONDUCTIVITY ELECTRORHEOLOGICAL MATERIALS

Technical Field

The present invention relates to certain fluid materials which exhibit substantial increases in flow resistance when exposed to electric fields. More specifically, the present invention relates to high strength electrorheological materials that utilize carrier fluids having a dielectric constant between about 3.0 and 7.5 and an observed conductivity less than about 1.00 x 10"? S/m.

Background Art

Fluid compositions which undergo a change in apparent viscosity in the presence of an electrical field are commonly referred to as electrorheological fluids or materials. Electrorheological materials normally are comprised of particles dispersed within a carrier fluid and in the presence of an electrical field, the particles become polarized and are thereby organized into chains of particles within the fluid. The chains of particles act to increase the apparent viscosity or flow resistance of the overall fluid and, in the absence of an electric field, the particles return to an unorganized or free state and the apparent viscosity or flow resistance of the overall material is correspondingly reduced.

An electrorheological fluid composed of a non-conductive solid dispersed within an oleaginous oil vehicle is described in U.S. Pat. No. 3,047, 507. The compositions contain a minimum amount of water and a minimum amount of a surface active dispersing agent, a non- conductive solid consisting of finely divided particles having an average diameter of from about 0.1 to about 5 microns, and an oleaginous oil vehicle having a viscosity not greater than that of lubricating oil and a dielectric constant between 2.0 to 5.5. In order to achieve the best performance, it is preferred that the dielectric constant of the oil component be as close to 2.0 as possible. Specific

examples given for the oil component include mineral oils, kerosene, polyoxyalkylene glycols, aliphatic esters, fluorinated hydrocarbons, and silicone oil.

European Patent Publication No. EP 0 311 984 A2 describes an electrorheological fluid containing a solid phase dispersed in a base liquid of a polyfluoroalkylmethylsiloxane. The solid phase can be derived from the lithium salt of a polymethacrylic acid while the base liquid can be polymethyl 3,3,3-trifluoropropylsiloxane.

U.S. Patent No. 3,367,872 and U.S. Patent No. 3,397,147 disclose electrorheological materials consisting of alumina or silica-alumina particles, a surface active agent and a high resistivity oleaginous vehicle having a dielectric constant less than 10, preferably between 2.0 to 5.5. Specific examples of the oleaginous vehicles disclosed include paraffin, olefin and aromatic hydrocarbons.

An electrorheological material that utilizes as the particle component a substantially anhydrous electronic conductor such as an organic semiconductor comprised of unsaturated, fused polycyclic systems containing conjugated π-bonds is disclosed in U.S. Patent No. 4,687,589. Specific examples of particle components include phthalocyanine-type compounds such as copper phthalocyanine, violanthrone B, porphin or azaporphin systems, poly(acene-quinone) polymers, and polymeric SchifFs Bases. Halogenated aromatic liquids are specified as the preferred continuous phase of the electrorheological material.

Electrorheological materials exhibiting low viscosity, low electrical conductivity, low toxicity and low freezing points are described in U.S. Patent No. 4,502,973. The composition of these materials include suspensions of a finely divided hydrophilic solid, such as solid polyhydric alcohols or cross-linked lithium polymethacrylate polymer salts, in a diaryl derivative as a hydrophobic liquid.

The utilization of electrorheological materials consisting of hydrophilic solids dispersed in a hydrophobic liquid is further

described in U.S. Patent No. 4,812,251. In this case the preferred hydrophobic liquid component comprises a mixture of a fluorosilicone whose average molecular weight is in the range of 200-700 A.M.U. (atomic mass unit) and polychlorotrifluorethylene (i.e., Fluorolube FS- 5, Hooker Chemical Co.), a high molecular weight fluorosilicone or a halogenated aromatic hydrocarbon. The addition of a low molecular weight fluorosilicone additive to another polymer is found to effectively reduce the viscosity of the overall fluid mixture.

Variations in the magnitude of the electrorheological effect have been observed for materials comprised of different particle and carrier components, such as those described above. In order for a material to polarize and respond as an electrorheological material, the particle and the carrier fluid must have different complex permittivities. The polarizability, β, of a particle in a fluid medium is given by:

β = (Eq. l)

[ε2+2ει]

where εi and ε<> are the complex permittivities of the carrier fluid and particle, respectively. By definition the complex permittivity is dependent upon both the dielectric constant (relative permittivity) and conductivity of the material. Any situation in which the polarizability of the particle is altered will inherently effect the observed electrorheological activity of the material. An explanation for the observed differences in electrorheological activity is also disclosed in U.S. Patent No. 5,075,021, which is incorporated herein by reference.

In general, the electrorheological activity of an electrorheological material has been found to increase proportionately with the dielectric constant of the carrier fluid, given a particle component having a fixed dielectric constant. However, when the dielectric constant of the carrier fluid becomes too high, the conductivity of the carrier fluid can reach unacceptably high levels so as to substantially interfere with the polarizability of the particle component and the overall electrorheological activity of the material.

An ideal carrier fluid for electrorheological materials therefore possesses a sufficiently high dielectric constant without an unacceptably high level of conductivity. A conductivity of less than about 1 x 10" S/m has been found to be acceptable for purposes of electrorheological activity.

It is also desirable that the continuous component or carrier fluid of an electrorheological material exhibit several other basic characteristics. These characteristics include: (a) chemical compatibility with both the particle component of the fluid and device materials; (b) low viscosity; (c) high dielectric breakdown strength; (d) relatively low cost; and (e) high density. Electrorheological materials should also be non-hazardous to the surrounding environment and, more importantly, be capable of functioning over a broad temperature range. Most of the carrier fluid components that are traditionally used in electrorheological materials as previously described cannot adequately meet all of these requirements. Specifically, many traditional electrorheological materials exhibit unacceptably high conductivities and unacceptably high viscosity variance over a given temperature range.

The selection of carrier and particle components for use in an electrorheological material is based on the minimum specifications for material properties, such as viscosity, dynamic yield stress, static yield stress, current density and response time, necessary to satisfy a particular application or device design. Since known carrier components do not exhibit all of the desirable attributes as previously mentioned, a need therefore exists for the development of new carrier fluids from which electrorheological materials can be prepared.

Disclosure of Invention

The present invention is an electrorheological material which exhibits an elevated level of electroactivity over a broad temperature range. More specifically, the present invention relates to electrorheological materials that utilize a newly discovered group of carrier fluids having a dielectric constant between about 3.0 and 7.5 and an observed conductivity less than about 1.00 x 10" ^ S/m. The

electrorheological materials of the invention comprise a carrier fluid and a particle component wherein the carrier fluid is selected from the group consisting of silicone copolymers, hindered ester compounds, and cyanoalkylsiloxane homopolymers, all of which are defined in more detail hereinafter.

The carrier fluids of the present invention are believed to have never before been utilized in electrorheological materials. The relatively high dielectric constant and correspondingly low conductivity of these carrier fluids are advantageous since it has been found that carrier fluids whose level of conductivity is greater than 1.00 x 10"? S/m begin to interfere with the polarizability of the particle component and the overall electrorheological activity of the material as described above. The present electrorheological materials also exhibit a minimal variance in viscosity over a broad temperature range. The utilization of the present carrier fluids in combination with known electroactive particles allows for the preparation of unique electrorheological materials that exhibit excellent rheological properties, as well as substantial electrorheological properties over a broad temperature range.

Best Mode for Carrying Out the Invention

The electrorheological materials of the invention comprise a carrier fluid and a particle component wherein the carrier fluid has a dielectric constant between about 3.0 and 7.5, an observed conductivity less than about 1 x 10"? S/m and is selected from the group consisting of silicone copolymers, hindered ester compounds, and cyanoalkylsiloxane homopolymers.

The silicone copolymers of the present invention are typically prepared through a multi-step process well familiar to those skilled in the art of silicone and organosilicon compounds. This process includes the co-hydrolysis of different low molecular weight organofunctional chloro- or alkoxy-silanes and -polysiloxanes to silanol intermediates. These intermediates rapidly co-condense to polymeric siloxane co-polymers. In addition to this hydrolysis process, the reaction of various chlorosilanes with alkoxysilanes,

acyloxysilanes, etc. can also lead to the formation of copolymers containing a siloxane backbone. A more complete description of the different synthetic methods employed in the the preparation of silicone copolymers is provided by W. Noll in "Chemistry and Technology of Silicones", Academic Press, New York, 1968 (the entire contents of which are herein incorporated by reference), hereinafter referred to as MΩll.

The silicone copolymers of the present invention can be represented by the formula:

R' R" R' R'

R ' - R '

wherein R', R", and R'" can independently be any straight chain, branched, cyclic or aromatic hydrocarbon radical, being halogenated or unhalogenated, and having from 1 to about 18, preferably 1 to about 6, carbon atoms; an ester group; an ether group; or a ketone group; with the proviso that at least one of R" and R'" is of a different functionality than R' and the further proviso that R" and R'" can also be a moiety wherein E is a highly electronegative atom or group, such as CN, CONH2, SH, Br, Cl, F, CF3 or NH2 and is preferably CN or CF3, and w is an integer from 2 to 8, preferably 2 to 4. It is presently preferred that at least one of R" and R ¹ " be a (CH2)wE group, while R' be a hydrocarbon radical. The number of the polymeric backbone units as specified by (y + z) can vary from 2 to 300, preferably from 10 to 150 with the proviso that x is an integer greater than or equal to 1 and y is an integer greater than or equal to 1.

Examples of silicone copolymers useful in the present invention include methyl-3,3,3-trifluoropropyl/dimethylsiloxanes, vinylmethyl/ dimethylsiloxanes, (aminoethylaminopropyl)methyl/ dimethylsiloxanes, (aminopropyDmethyl/dimethylsiloxanes, (acryl- oxypropyDmethyl/dimethylsiloxanes, (methylacryloxypropyl)methyl dimethylsiloxanes, (mercaptopropyDmethyl/dimethylsiloxanes, (chloromethylphenethyDmethyl/dimethylsiloxanes, (cyanopropyl)-

methyl/dimethylsiloxanes, (cyanopropyDmethyl/methylphenylsilox- anes, glycidoxypropylmethyl/dimethylsiloxanes, methylphenyl/ dimethylsiloxanes, (tetrachlorophenyD/dimethylsiloxanes, diphenyl dimethylsiloxanes, methyloctadecyl/dimethylsiloxanes, methyloctyl/ vinylmethyl/dimethylsiloxanes, (mercaptoethyl)methyl/dimethylsilox- anes, (cyanoethyDmethyl dimethylsiloxanes, and ethylene oxide/ dimethylsiloxanes, with methyl-3,3,3-trifluoropropyl/dimethylsilox- anes, (cyanopropyDmethyl/dimethylsiloxanes, and methylphenyl/ dimethylsiloxanes being preferred.

Many of the silicone copolymers of the invention are commercially available. These silicone copolymers are typically prepared by the previously described methods, as well as by the procedures more fully disclosed in Noll. The viscosity of commercially obtainable copolymers can be adjusted by techniques well known to those skilled in the art of manufacturing silicone and organosilicon compounds. Such techniques include thermal depolymerization at high temperatures and reduced pressures, as well as both acid and base depolymerization in the presence of an appropriate endblocking agent, such as hexamethyldisiloxane.

The hindered ester compounds of the present invention can be based on pentaerythritol or a trimesic ester. The pentaerythritol-based hindered ester compounds of the invention correspond to the following formula:

COOR

CH ₉ I ROOC - H ₂ C - C - CH ₂ - COOR

CH ₂

COOR

wherein R is the same or different and can be any straight chain, branched, or cyclic hydrocarbon radical having from 1 to about 25, preferably 1 to about 18, carbon atoms. R is preferably a straight chain hydrocarbon radical.

The trimesic ester-based hindered ester compounds of the invention correspond to the following formula:

wherein R is as defined above. In addition, the ring structure can be a saturated or non-aromatic six-carbon ring, although aromaticity is preferred.

Many of the hindered ester compounds of the invention are commercially available. Ester compounds are typically prepared using solvolytic reactions, such as direct esterification of organic acids (i.e., fatty acids, etc.), alkylation of carboxylate salts, trans- esterification, and the alcoholysis of acyl halides, anhydrides, ketenes, nitriles and amides, as well as using either condensation reactions or free radical processes. Specific examples of ester compounds formed through the reaction of pentaerythritol with methacrylic acid, adipic acids, maleated rosin and various fatty acids are known. A more complete description of the various methods employed in the synthesis of organic esters is provided by M. Ogliaruso and J. Wolfe in "Synthesis of Carboxylic Acids, Esters and Their Derivatives" (John Wiley & Sons, New York, 1991), the entire contents of which are incorporated herein by reference.

The hindered ester compounds of the invention typically have a dielectric constant between about 3 and 5 and a conductivity less than about 4.0 x 10" 10 S/m. Due to their slightly higher dielectric constants, the trimesic ester-based compounds are presently preferred over the pentaerythritol-based hindered ester compounds for use in the invention. A more complete description of the properties associated with hindered ester compounds is provided by F. Waddington in "High Temperature Esters: New Dielectric Fluids for Power Engineering Applications" (GEC Journal of Science and Technology. 49 (1), 1983, pp. 18-22), which is incorporated herein by reference.

The cyanoalkylsiloxane homopolymers of the present invention can be represented by the formula:

wherein R' and R" are the same or different and can be any straight chain, branched, cyclic or aromatic hydrocarbon radical, being halogenated or unhalogenated, and having from 1 to about 18, preferably 1 to about 6, carbon atoms; an ester group; an ether group; or a ketone group, with the proviso that R" can also be a (CH2)wCN moiety. R ^* and R" are preferably a straight chain hydrocarbon radical, with a methyl group being most preferred. The length, w, of the alkyl chain connecting the cyano group to the siloxane backbone of the homopolymer can range from 2 to 8, preferably 2 to 4. The number of the polymeric backbone units as specified by x can vary from 1 to 300, preferably 10 to 150.

Examples of cyanoalkylsiloxane homopolymers include polybis(cyanopropyl)siloxanes, polymethylcyanopropylsiloxanes, poly- methyl cyanoethylsiloxanes, and amine terminated polymethyl- cyanoethylsiloxanes, with polymethylcyanopropylsiloxanes being specifically preferred. Several cyanoalkylsiloxanes appropriate to the present invention are commercially available. These homopolymers are typically prepared through catalyzed hydrosilation reactions between polyorganohydrosiloxanes and alkene cyanide compounds, such as allyl cyanide. They also can be prepared through procedures similar to those previously described for the synthesis of silicone copolymers. The various methods for preparing cyanoalkylsiloxane homopolymers are well familiar to those skilled in the art of silicones and organosilicon compounds. A more complete description of the the different synthetic methods employed in the the preparation of silicone homopolymers is provided in Noll.

Due to their ability to exhibit a minimum change in viscosity, dielectric constant, and conductivity over a broad temperature range, the silicone copolymers are, in general, the preferred carrier fluids for use in the present invention.

The carrier fluids of the present invention typically have a viscosity that is between about 0.5 and 1000 mPa-s, preferably between about 5 and 150 mPa-s. The carrier fluid of the present invention is typically utilized in an amount ranging from about 50 to 95, preferably from about 60 to 85, percent by volume of the total electrorheological material. This corresponds to approximately 19 to 82, preferably 26 to 57, percent by weight when the carrier fluid and particle of the electrorheological material have a specific gravity of about 1.0 and 4.3, respectively.

The particle component can essentially be any solid which is known to exhibit electrorheological activity. Typical particle components useful in the present invention include amorphous silicas, synthetic silicas, precipitated silicas, fumed silicas, silicates, aluminum silicates, ion exchange resins and other inorganic particles known in the art such as those composed of titanium dioxide, barium titanate, lithium hydrazinium sulfate and insulated metallic particulates. Other typical particle components useful in the present invention include polyvinyl alcohols, polyhydric alcohols, silicone ionomer reaction products, monosaccharides, porphin systems, metallo-porphin systems, poly(acene-quinone) polymers, polymeric Schiff bases, anionic surfactants, polyelectrolytes, carbonaceous particulates, and other organic and polymeric particles known in the art such as those composed of polymethacrylic acid salts and copolymers of phenol, aldehydes, olefins, ethers and/or acids. The particle component may also be ionic and non-ionic dyes, such as those described in U.S. patent application Serial Nos. 07/806,981 and 07/852,586 entitled "Ionic Dye-Based Electrorheological Materials" and "Colorant-Containing Electrorheological Materials," respectively, the entire contents of which are incorporated herein by reference. The preferred particle components of the present invention include insulated metallic particles, as well as atomically polarizable

paraelectric particles such as those described in U.S. Patent Application Serial No. 07/829,137 entitled "Atomically Polarizable Electrorheological Materials," the disclosure of which is incorporated herein by reference.

The diameter of the particles utilized herein can range from about 0.1 to about 500 μm and preferably from about 1.0 to about 50 μm. The particle component typically comprises from about 5 to 50, preferably 15 to about 40, percent by volume of the total composition depending on the desired electroactivity and viscosity of the overall material. This corresponds to approximately 18 to 81, preferably 43 to about 74, percent by weight when the carrier fluid and particle of the electrorheological material have a specific gravity of about 1.0 and 4.3, respectively.

The electrorheological material of the present invention may contain a small amount of an activator in combination with the particle component. However, in order to effectively operate over a broad temperature range, it is preferred that no activator be used in the present invention. Typical activators for optional use in the present invention include water and other molecules containing hydroxyl, carboxyl or amine functionality. Typical activators other than water include methyl, ethyl, propyl, isopropyl, butyl and hexyl alcohols; ethylene glycol; diethylene glycol; propylene glycol; glycerol; formic, acetic, sulfuric and lactic acids; aliphatic, aromatic and heterocyclic amines, including primary, secondary and tertiary amino alcohols and amino esters that have from 1-16 atoms of carbon in the molecule; methyl, butyl, octyl, dodecyl, hexadecyl, diethyl, diisopropyl and dibutyl amines; ethanolamine; propanolamine; ethoxyethylamine; dioctylamine; triethylamine; trimethylamine; tributylamine; ethylene-diamine; propylene-diamine; triethanol- amine; triethylenetetramine; pyridine; morpholine; imidazole; and mixtures thereof. Water is the preferred activator for optional use in the present invention. When employed, the activator is utilized in an amount from about 0.1 to about 10, preferably from about 0.5 to about 5.0, percent by weight relative to the weight of the particle component.

A surfactant to disperse the particle component may also be utilized in the present invention. Such surfactants include known surfactants or dispersing agents such as glycerol monooleate, sorbitan sesquioleate, stearates, laurates, fatty acids, fatty alcohols, and the other surface active agents discussed in U.S. Patent No. 3,047,507 (incorporated herein by reference) but preferably comprise non-ionic surfactants such as the steric stabilizing amino-functional, hydroxy- functional, acetoxy-functional, or alkoxy-functional polysiloxanes such as those disclosed in U.S. Patent No. 4,645,614 (incorporated herein by reference). Other steric stabilizers such as graft and block copolymers may be utilized as a surfactant for the present invention and such other steric stabilizers as, for example, block copolymers of polyethylene oxide) and poly(propylene oxide) are disclosed in detail in U.S. Patent No. 4,772,407 (incorporated herein by reference) and in Napper, "Polymeric Stabilization of Colloidal Dispersions," Academic Press, London, 1983 (incorporated herein by reference). Still other steric stabilizers include hyperdispersants, such as HYPERMER® (ICI Americas, Inc.) and SOLSPERSE® (ICI Americas, Inc.) hyperdispersants, fluoroaliphatic polymeric esters, such as FC-430 (3M Corporation), and titanate, aluminate or zirconate coupling agents, such as KEN-REACT® (Kenrich Petrochemicals, Inc.) coupling agents.

The surfactant, if utilized, is preferably an amino-functional polydimethylsiloxane, a fluoroaliphatic polymeric ester, a hyper- dispersant or a coupling agent. The optional surfactant may be employed in an amount ranging from about 0.1 to 20 percent by weight relative to the weight of the particle component.

The electrorheological materials of the present invention can be prepared by simply mixing together the carrier fluid, the particle component and surfactant. If the presence of water as an activator is to be minimized, the corresponding electrorheological material is preferably prepared by drying the particle component in a convection oven at a temperature of from about 110°C to about 150°C for a period of time from about 3 hours to about 24 hours. The ingredients of the electrorheological materials may be initially mixed together by hand

with a spatula or the like and then subsequently more thoroughly mixed with a mechanical mixer or shaker or dispersed with an appropriate milling device such as a ball mill, sand mill, attritor mill, paint mill, or the like, in order to create smaller particles and a more stable suspension.

Evaluation of the mechanical/electrical properties and characteristics of the electrorheological materials of the present invention, as well as other electrorheological materials, can be obtained through the use of concentric cylinder couette rheometry. The theory which provides the basis for this technique is adequately described by S. Oka in Rheology, Theory and Applications (volume 3, F. R. Eirich, ed., Academic Press: New York (1960), pages 17-82) which is incorporated herein by reference. The information that can be obtained from a concentric cylinder rheometer includes data relating mechanical shear stress to shear strain, the static yield stress and the electrical current density as a function of shear rate. For electrorheological materials, the shear stress versus shear rate data can be modeled after a Bingham plastic in order to determine the dynamic yield stress and viscosity. Within the confines of this model, the dynamic yield stress for the electrorheological material corresponds to the zero-rate intercept of a linear regression curve fit to the measured data. The electrorheological effect at a particular electric field can be further defined as the difference between the dynamic yield stress measured at that electric field and the dynamic yield stress measured when no electric field is present. The test geometry that is utilized by these rheometers for the characterization of electrorheological materials is a simple concentric cylinder couette cell configuration. The material is placed in the annulus formed between an inner cylinder of radius Ri and an outer cylinder of radius R2- One of the cylinders is then rotated with an angular velocity CO while the other cylinder is held motionless. The relationship between the shear stress and the shear strain rate is then derived from this angular velocity and the torque, T, applied to maintain or resist it.

The dielectric properties of electrorheological materials of the present invention, as well as other electrorheological materials, can be

obtained through the use of impedance spectroscopy. The impedance parameters that are typically measured include capacitance and conductance. From these parameters, the dielectric constant, dielectric loss factor, loss tangent and conductivity of the electro- rheological material can be calculated. A more complete description of the applicability of this technique to the measurement of the dielectric spectra for electro-rheological materials is provided by Weiss and Carlson in the "Proceedings of the Third International Conference on Electrorheological Fluids" (ed., R. Tao, World Scientific Publishing Co., London, 1992, pp. 264-279), the entire disclosure of which is incorporated herein by reference.

The following examples are given to illustrate the invention and should not be construed to limit the scope of the invention.

Viscosity Redyςtion for Fluorinated Silicone Copolymer To a reaction flask equipped with a magnetic stir bar is added

500 mL of 118 cstk (50%)-methyl-3,3,3-trifluoroρropylsiloxane-(50%) dimethyl-siloxane copolymer (PS187, Huls America Inc.), 108 g of concentrated sulfuric acid (Aldrich Chemical Co.) and 51.0 g hexamethyldisiloxane (99.95%, Aldrich Chemical Co.). The reaction flask is then fitted with a drying tube. The reaction mixture is stirred for five days at room temperature. A total of 100 mL of distilled deionized water is added to the reaction mixture. After stirring for two hours, the organic layer is removed and washed three times with 100 mL portions of distilled deionized water, four times with 40 mL portions of 10% sodium bicarbonate solution and seven times with 100 mL portions of distilled deionized water. Any excess hexa¬ methyldisiloxane is removed under reduced pressure at 60°C. The resulting (50%)-methyl-3,3,3-trifluoropropylsiloxane-(50%) dimethyl- siloxane copolymer is characterized by infrared spectroscopy and ^C nuclear magnetic resonance spectroscopy. The viscosity of the fluid is measured using concentric cylinder rheometry to be 21 cstk. The dielectric constant and conductivity of the copolymer are measured through the use of impedance spectroscopy to be 5.31 and 2.6 x 10"9 S/m, respectively, at an A.C. field frequency of 1.0 kHz. The copolymer is stored in a polyethylene bottle until used in Example 1.

Example 1

An electrorheological material is prepared by combining 50.04 g of titanium dioxide (Ti-Pure® R960, E. I. Du Pont de Nemours & Co.), 43.46 g of the (50%)-methyl-3,3,3-trifluoropropylsiloxane-(50%) dimethylsiloxane copolymer prepared above, and 1.03 g of isopropyltri(dioctyl)phosphato titanate (KEN-REACT® KR12, Kenrich Petrochemical Inc.). The resulting combination of ingredients is thoroughly dispersed using a high speed disperser equipped with a 16- tooth rotary head. Before use, the titanium dioxide particles are oven- dried in a convection oven for 16 hours at a temperature of 125°C. The use of these weight amounts of ingredients corresponds to an electrorheological material containing 25 volume percent titanium dioxide particles. The electrorheological material is stored in a polyethylene bottle until mechanical and electrical properties can be tested.

Example 3

An electrorheological material is prepared in accordance with Example 1 utilizing 30.23 g Ti-Pure® R960, 0.60 g KEN-REACT® KR12 and 22.94 g of (10-12)% cyanopropylmethyl - (88-90)% dimethyl siloxane copolymer (PS908, Huls America Inc.). The dielectric constant and conductivity of the cyanopropylmethyl/dimethylsiloxane copolymer are measured through the use of impedance spectroscopy to be 5.89 and 3.6 x 10"9 S/m, respectively, at an A.C. field frequency of 1.0 kHz.

Example 3

An electrorheological material is prepared in accordance with

Example 1 utilizing 50.04 g Ti-Pure® R960, 1.00 g KEN-REACT® KR12 and 34.49 g of a trimesic ester-based fluid (MIDEL® 7221, Micanite & Insulators Co., Ltd., Manchester, Great Britian). The dielectric constant and conductivity of the trimesic ester-based oil are measured through the use of impedance spectroscopy to be 4.27 and 4.0 x 10- ¹⁰ S/m at an A.C. field frequency of 1.0 kHz.

Electrorheological Activity at 25°C

The dynamic electrorheological properties (25°C) of the electrorheological materials prepared in Examples 1-3 are measured using concentric cylinder couette cell rheometry at an A.C. electric field of 2.0 kV/mm and a frequency of 1000 Hz. As shown in Table 1 below, all electrorheological materials are observed to exhibit a substantial electrorheological effect. The electrorheological effect is defined as the difference between the dynamic yield stress measured at an electric field strength of 2.0 kV/mm and the dynamic yield stress measured when no electric field is present.

Electrorheological Activity at 100°C

The dynamic electrorheological properties (100°C) of Examples 1-3 are measured using concentric cylinder couette cell rheometry at an A.C. electric field of 2.0 kV/mm and a frequency of 1000 Hz. As shown in Table 2 below, all electrorheological materials are observed to exhibit a substantial electrorheological effect at this elevated temperature.

As can be seen from the above data, the electrorheological materials of the present invention are capable of exhibiting substantial electrorheological activity over a broad temperature range.